Head-mounted augmented reality display

ABSTRACT

Compact and low mass augmented and fully virtual head mounted display designs are disclosed. The disclosed displays employ a display located between the eye and the main optical element of the head mounted display. These designs additionally afford the ability to support augmented reality displays because the user can see both the virtual image from the display and the real world if desired. The designs use semi-transparent displays where either the display emits circularly polarized light or the displays which emits light from one surface or the view of the display directly from the eye is obscured.

This application is a continuation of U.S. application Ser. No.17/222,857, filed Apr. 5, 2021, which is a continuation of U.S.application Ser. No. 16/057,327, filed Aug. 7, 2018, now U.S. Pat. No.10,969,587, which is a continuation of U.S. application Ser. No.15/445,624, filed Feb. 28, 2017, now U.S. Pat. No. 10,042,167, which isa continuation of U.S. application Ser. No. 14/749,568, filed Jun. 24,2015, now U.S. Pat. No. 9,581,821, which claims priority to U.S.Provisional Application 61/998,306, filed Jun. 24, 2014.

FIELD OF THE INVENTIONS

The inventions described below relate to the design of augmented andvirtual reality head mounted displays and particularly displays whichuse reflective optics to create a virtual image to be seen by a user,often in stereo with a separate image for each eye.

BACKGROUND OF THE INVENTIONS

One approach for head-mounted virtual reality displays has been to use aFerrand Pancake Window™ as described in U.S. Pat. No. 3,443,858 andfollow-on devices which simply make the design more light efficient.This design is shown in FIG. 1. Underlying this design is therecognition that a curved mirror can be used to achieve short focallengths with large diameters thus offering wide fields of view.Additionally, the pancake window can be made to be semi-transparent byreplacing the display with a 45 degree 50% reflective mirror andadditional optics in front of the display which is folded out of theoptical path to form a real image of the display where the pancake isfocused; the refractive path through the pancake and the 45 degreemirror offer a view into the real world and because the power from thepancake comes from the reflective surface, it can be buried in aplano-plano doublet or as an interior partially reflective surface. Theoptical path of the pancake window device uses circular polarizationbased mirror bounces to generate a virtual image of the display seenfrom the eye side of the optics. The eye sees light which was, duringthe optical path, traveling away from the eye.

SUMMARY

The devices and methods described below provide for an augmented orvirtual reality head mounted display with the display interposed betweenthe user's eye and a curved reflector. In this head mounted displaysystem, positioning the display between the user's eye and thereflective element enables heavy optical components to be located closerto the user allowing a smaller display to provide a wide field of view.The curved reflector may be aspherical or spherical.

An augmented reality display includes a curved reflector and an opticalstack oriented between the curved reflector and a user's eye. Theoptical stack consists of a display, a quarter wave plate and areflective polarizer.

An augmented or virtual reality display may include two or more displayslocated at different distances from the user's eye while still remainingbetween the user's eye and the reflective optics. Multiple displays atdifferent distances enable the user to perceive virtual images atdifferent apparent distances from the user's eye. This configurationaddresses the visual conflict between the eye's accommodation andvergence. Displays which address both accommodation and vergence feelvisually ‘correct’.

An augmented or virtual reality display may also include one or moreelements such as a liquid crystal display to optically occlude, ondemand, all or part of the real world. This real world occlusion can beturned on and off electronically. Such a configuration also enables thepartial occlusion of the real world—for example enabling part of thereal world to be dimmed and the virtual objects that reside at theangular position in the user's field of view to be brighter than thedimmed real world. Through careful manipulation of the relativebrightness of the dimmed real world and the virtual one, a seamlessmixed reality environment may be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art image-forming apparatus.

FIG. 2 is an exploded view of the optical elements of an augmentedreality head-mounted display.

FIG. 3 is a side view of the augmented reality head-mounted display ofFIG. 2.

FIG. 4 is a detailed cross section of the optical elements of thedisplay system of FIG. 3.

FIG. 5 is a diagram of a display system which creates virtual images atdifferent apparent distances from the eye.

FIG. 6 is a diagram of an alternate display system.

FIG. 7 is a detailed cross section of the reflector and external opticalelements of the display system of FIG. 6.

FIG. 8 is an exploded view of the optical elements of the augmentedreality head-mounted display of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTIONS

FIGS. 2, 3 and 4 illustrate augmented reality head-mounted display 10.Display 10 includes optical element and display stack 12 located betweenuser's eye 1 and reflector 13 to permit the user to simultaneously viewa portion of light 5 emitted or reflected from the real-world, such asfrom mascot 3, and a portion of light from the virtual world such aslight 15 from emissive display 14. Reflector 13 may be any suitablecurved reflector having a spherical or aspherical or compound shape.Emissive display 14 emits circularly polarized light 15 toward user eye1. Emissive display may be any suitable emissive display which emitslight from its surface (or from within a sheet of material of less thana few millimeters thick). The actual construction of such a displaymight use organic light emitting diodes (OLED), light emitting diodes(LED) or any other suitable means to produce a plurality of lightemitting elements which can be arranged as a generally transparentelement on a substantially locally continuous surface such as anedge-illuminated element and a liquid crystal display (LCD). Emissivedisplay 14 is also transparent or semi-transparent and that transparencycan be either an overall general passing of light or may be more like adot type beam splitter where there are small non transparent elements ona largely transparent substrate so that the overall effect is that thedisplay does allow light to pass through it.

FIG. 3 illustrates a detailed cross section of the optical elements ofdisplay system 10 showing emitted light 15 passes through quarter-waveplate 16 becoming linearly polarized light 17. Polarized light 17 thenreflects off reflective polarizer 18 on the surface of element 20 andreflected polarized light 17R passes back through quarter-wave plate 16and is circularly polarized to have the same polarization state as light15 that originally emanated from emissive display 14. Reflected andcircularly polarized light 21 then passes through emissive display 14.Thus, secondary light 15S which emanates from emissive display 14towards reflector 13 and the reflected and circularly polarized light 21(having traversed quarter-wave plate 16 twice) have the same circularpolarization and are thus indistinguishable. Reflected and circularlypolarized light 21 as well as secondary light 15S then reflects fromsurface 13A and some portion (perhaps substantially all) is reflected aslight 22. Reflector 13 is idealized. In practice, reflector 13 is formedto meet the visual performance goals, manufacturing constraints, and theindustrial design.

Upon reflection from reflector 13 the handedness of light 15S and 21 areboth reversed and they are illustrated as light 22 which now passes backthrough emissive display 14 and quarter-wave plate 16 becoming light 23with a linear polarization orthogonal to light 17 and light 23 passesthrough reflective polarizer 18 and optical element 20 and can be seenby eye 1 at or near eye-box 28. In this way, the light passing throughreflective polarizer 18 (and optical element 20) is light which has comefrom the display and has been reflected from the reflector 13. Theproportion of light reflected by the mirrored surface can be adjustedfrom substantially all the light reflected to only a small portion ofthe light being reflected and adjusting that parameter allows thedesigner to control the relative brightness of the reflected display 14.

An optional absorbing linear polarizer, polarizer 19, may be included toallow only light with the sense of linear polarization associated withthe light 23 to pass through and absorbs the other which largely arisesfrom light which is reflected by the user's eye or enters the displayfrom the eye side of the optics. The final linear polarizer such aspolarizer 19 is optional. If reflective polarizer 18 has a dark surfacewith a protective layer, final absorbing polarizer 19 need not be used.

The thickness of emissive display 14, quarter-wave plate 16, reflectivepolarizer 18 and optical element 20 is arbitrary and for illustrativepurpose, ideally some or all of these are formed as thin sheets,particularly quarter-wave plate 16. If there is a significant thicknessto quarter-wave plate 16 then the light from the front and back sides ofthe display will be focused at slightly different places in space fromthe user's point of view. This is not a significant issue asquarter-wave films can be quite thin and the thickness they introducemay be beneficial for improving the visual feel of the display system.

In display system 10 and the systems described below which have linearlypolarized light emerging to the user's eye, the contrast ratio can besomewhat improved by removing light which reflects off the viewers eye 1back into the optical system and display. This may be accomplished byadding a quarter-wave plate to the final absorbing linear polarizer.Thus the linearly polarized light which passes towards the eye iscircularly polarized and the reflected light returning from the eye willhave some portion that is reversed in handedness which becomesorthogonally polarized relative to linear absorbing polarizer 19 and isthus absorbed.

An optional element such as LCD element 24 may be incorporated into orsecured to reflector 13 to block light from the real world. LCD element24 could be formed onto the surface of reflector 13 or separate from it.A suitable LCD element is composed of a plurality of pixels which areelectronically controlled to adopt a transparent or an opaque state. LCDelement 24 may be composed of polarizers, liquid crystal material, and aquarter-wave plate ideally affording the designer the ability to (basedon the pixel matrix of the LCD element) to have light 5 from the realworld pass through element 24 and either be absorbed by the polarizersof LCD 24 or to emerge through element 24 imparted with circularpolarization indistinguishable from light 22 which passes throughoptical element and display stack 12 and into the eye 1.

Quarter-wave plates such as quarter-wave plate 16 are used in thisdescription and in this context with an emissive display means that,when appropriately oriented, the quarter-wave plate converts linearlypolarized light to substantially circularly polarized light and may bereferred to as an achromatic quarter-wave plate. A suitable quarter-waveplate performs as a substantially achromatic quarter-wave plate over theentire range of wavelengths of interest or it behaves substantially as aquarter-wave plate for the wavelength ranges of interest or thoseemitted by the display. For example, if a display has primary colors of460 nm, 510 nm, and 625 nm with these containing most of the emittedenergy within a +/−5 nm range the quarter-wave plate might be designedeither to be substantially achromatic (i.e. with some tolerance) overthe range 455 nm to 630 nm or it might be designed only to induce aquarter-wave of retardance (+/− some tolerance) over the ranges of 455to 465 nm; 505 to 515 nm; and 620 to 630 nm with the performance of theelement either relaxed, undefined, or specified to some other degree ofretardation in the other portions of the visible spectrum. Similarly,the performance of the quarter-wave plates will also be defined oversome cone angle which will be selected based on the cone of emissionfrom the display such as emission cone 26 in FIG. 3. In thisdescription, quarter-wave plate is to be understood as a quarter-waveplate which performs that function over the wavelengths of interest,even if the word achromatic is absent.

A reflective polarizer as discussed herein, such as reflective polarizer18, has the property of reflecting one linear state of polarization andreflecting orthogonally polarized light. A suitable polarizer may be awire grid polarizer such as those made by Moxtek or they may beimplemented with a plastic film type material made by 3M and others withsimilar properties, or by other means which have substantially the sameproperty of behaving substantially as a mirror to one linearpolarization state and as a semi-transparent window to orthogonallypolarized light. The disclosed wire grid polarizer or other similarelement when combined with a quarter-wave plate makes a combined elementwhich substantially reflects one state of circularly polarized light andsubstantially transmits orthogonally polarized light. This pair ofelements may be replaced with any suitable single element which has thesame properties with respect to circularly polarized light. Examples ofsuch elements have been made with cholesteric liquid crystals forexample and can be expected to be made using nano-fabrication techniquescreating chiral meta-materials or chiral mirrors which reflect onecircular polarization state and transmit the other for either a range ofwavelengths in the visible or for selected relevant wavelength ranges.When the majority or substantially all the light from an emissivedisplay is emitted toward the concave reflector or mirror, a linearpolarizer is not required as illustrated with respect to FIG. 3 below.However, when the majority or substantially all the light from anemissive display is emitted toward the user's eye, a linear polarizer isrequired as illustrated in FIG. 1.

Display system 30 of FIG. 2 creates virtual images 31A, 31B and 31C atdifferent apparent distances from user's eye 1 from the illustratedpencils of light from displays 32, 34 and 36. Circularly polarized lightemanates from the eye side, sides 32E, 34E and 36E respectively, ofemissive displays 32, 34, and 36 which are each oriented at differentdistances from user's eye 1, distances 33A, 35A and 37A respectively, aswell as at different distances from reflective surface 38A, distances33B, 35B and 37B respectively, to generate different virtual images 31A,31B and 31C at different apparent distances from the user's eye.Emissive displays emit light with a very wide cone angle and theillustrations herein illustrate a pencil of emitted light whichrepresents the light emitted from the display.

As discussed above, emitted light from each emissive display passesthrough achromatic quarter-wave plate 39 becoming linearly polarizedlight. The polarized light then reflects off reflective polarizer 40 onthe surface of element 41 and the reflected polarized light passes backthrough quarter-wave plate 39 and is circularly polarized to have thesame polarization state as the light that originally emanated from eachemissive display. The reflected and circularly polarized light thenpasses back through each emissive display (32, 34 and 36). Thus, light42 which travels toward reflector 38 is comprised of light from each ofthe three displays 32, 34 and 36 having reflected off surface 38A. Light42 is illustrative of all the light from each of the displays and iscircularly polarized light such as light 44 (having traversedquarter-wave plate 39 twice and reflected from reflective polarizer 40)have the same circular polarization and are thus indistinguishable.Reflected and circularly polarized light 42 then reflects from surface38A and some portion (perhaps substantially all) is reflected as light47. Similarly, light 44 is reflected as light 45. This descriptionapplies to light from all three emissive displays.

Upon reflection at surface 38A, the handedness of the light 42 and 44 isreversed in light 45 and 45 respectively. Light reflected from reflectorsurface 38A such as light 45 and 45 now passes back through emissivedisplays 36, 34 and 32 and quarter-wave plate 39 and on this pass it hasa linear polarization state orthogonal to the light originally passingthrough quarter-wave plate 39 from the emissive displays. The lightreflected from reflector surface 38A such as light 45 and 45 now passesthrough reflective polarizer 39 and optical element 40 and can be seenby user's eye 1 in eye-box 48.

Emissive displays 32, 34 and 36 are displaced from each other such thatthey form different virtual images as perceived by the user's eye ateye-box 48. The displays here are shown parallel to each other but theplanes formed by the displays may be tilted if desired by tilting thedisplay surfaces. To reduce inter reflections, the displays may beanti-reflection coated or the space between the displays may be filledwith a transparent medium which index matches better than air; forexample, if glass or plastics were used, they would likely be laminatedto the displays.

In a simpler display, system light emanates from one face of atransparent display and travels through a substantially transparentmaterial such as air, plastic, or glass to a partially reflectiveconcave mirrored surface. The light is partly reflected at the mirroredsurface and some light is lost. The reflected light passes back throughthe air or glass towards the display and then through the display to theviewer's eye.

Virtual display 50 of FIGS. 6, 7 and 8 employs an emissive display,display 52, which is generally transparent and emits light 55 from oneface or surface, emissive surface 52S which is oriented with display 52between emissive surface 52S and user's eye 1. Light 55 then encountersthe interior surface 56A of concave reflector or mirror shell 56. Mirror56 is shown as having thickness and the actual reflective/transmissivecoating 58 is typically applied on the inside or interior surface 56Awhich affords some protection to the coating if the outside or exteriorsurface of 56B is the external surface of the display system. Light 55impinges on reflective surface 58 and some portion of the light 55R; asdetermined by the reflective/transmissive characteristics 58X ofreflective surface coating 58 is reflected back to the user's eye 1.Reflected light 55R passes back through display 52 which is largely orat least partially transmissive. Reflected light 55R may also(optionally) pass through occluding layer 54 which may provide a lightblocking pattern of small opaque shapes 59X such as pattern 59 locatedsuch that any light from display 52 such as light 52X which emanates inthe direction of the eye may be blocked from view. The position of theopaque shapes can be optimized to account for the parallax between theemissive element and the user's eye. The pattern of occluding shapescould be on a thin LCD formed on the eye side of the emissive display.Light blocking pattern 59 may also be any linear elements such as lines,or any other suitable shapes or combination of shapes. The pattern ofopaque shapes may also preferentially block the light by adopting anysuitable halftone pattern.

Reflective coatings such as reflective coating 58 or 38A may be appliedto the inside or the outside of the curved shell such as shell 56. Thethickness of shell 56 can vary for example, to account for the user'sophthalmic prescription. The reflective surface or coating can bewavelength tuned to match the spectral characteristics of the emissivedisplay or displays and by tuning the ratio, one can achieve betterrelative brightness with a low power display by wasting less light.Additionally, the reflector shells may be formed as a Fresnel typereflector. Note that the surfaces of the reflector would optimally havefacets which, from the eye's point of view are concentric.

Any of display systems 10, 30 or 50 may include one or more opticalelements on the exterior of the reflector element as illustrated inFIGS. 6, 7 and 8. External optical elements such as linear polarizer 60and a quarter-wave plate 62 properly polarize light from outside any ofdisplay systems 10, 30 or 50 and impinging external light such as light53 of FIG. 3 will pass through linear polarizer 60 and quarter-waveplate 62 so that light 53X arriving from outside display system 50 hasthe same sense of circular polarization as light 55R reflected from theinterior surface of the mirror. In that way, the optical systems aretransmissive.

Polarization elements may be placed on the outside or exterior surfaceof the augmented reality display to allow external light in and toreduce the amount of light from the display that escapes through thereflector. Orienting the polarization elements on the outside requirescurved reflector 56 to be interposed between the polarization elementsand the user's eye. Light from inside the optical system, between theuser's eye and the curved reflector, which passes through reflectivemirror coating 58 such as light 55X must pass through quarter-wave plate62 and will become linearly polarized light 55L which will be absorbedby external linear polarizer 60 on the outside of the system. Thus, fromthat side of the system little to no light from the display is visible.This same technique applies to the display shown in FIGS. 3, 4, and 5.

Similarly, augmented reality displays may use mirrors and partiallytransparent/partially reflecting mirrors. These optical elements may beimplemented either with coatings such that their reflective/transmissiveproperties behave as substantially broadband devices in the visiblespectrum over which the display illumination is relevant or may beconstructed using coatings which are selective in terms of thewavelengths (technically selected ranges of wavelengths) of light wherethe particular reflective/transmissive behavior is tailored to match insome way the wavelength ranges emitted by the display.

Where present, the term concave mirror is to be understood that thedetailed sag and shape of the surface and optical properties of thatsurface would be chosen to meet particular performance requirements inthe product design. For example, the surface could be a simple sphericalshape, an aspherical shape, or a free form optical surface and thedesigner would optimize the shape based on performance requirements suchas field of view, manufacturing method, and the aesthetic requirementsof the product design. The mirrored or reflective surface can be made asa concave shell, a concave shell with no optical power, or aprescription surface on the inside/outside surface. The surfaces andmaterial can be selected and or made to account for vision of theindividual person.

A display panel or emissive display emits light which is substantiallycircularly polarized with a particular handedness. The light emanatingfrom the display passes through a circular polarizer and becomeslinearly polarized. The linearly polarized light then is reflected by amirror which reflects one state of linear polarization and passes theother. The linearly polarized light is thus reflected back towards thedisplay and again passes through the quarter-wave plate and iscircularly polarized with the same handedness as before. It then passesthrough the display panel which is largely transparent and emerges stillcircularly polarized with a particular handedness. The light thentraverses through air, glass or plastic to a concave mirrored surface.At the mirrored surface, some light passes through and is lost, theother light is reflected and as a result of the reflection has theopposite sense of circular polarization. The light then passes throughthe display, which is largely transparent and then through theachromatic quarter-wave plate linearly polarizing the light with alinear state of polarization which is perpendicular to the linear stateof polarization the light had initially at this surface and since thelinear polarizer reflects only one linear state, this light istransmitted through the linear polarizer. The light then, optionally,passes through an absorbing type polarizer and emerges from the displaysystem. Alternatively, the displays can be curved in a cylindrical form.Emissive displays such as displays 14, 32, 34, 36 and 52 may be anysuitable light emitting display as discussed above withreflective/absorbing/interference creating/nano structures to force thelight to emanate from one side.

An OLED type display on a thin substrate where the light emanates fromboth sides of the emissive material may be made to emit light primarilyfrom a single side. For example, OLED displays have been made withpatterns similar to a dot type beam splitter except the structure isdescribed as using stripes instead of dots. For the applicationsdescribed here, patterns of dots would be more advantageous and could beapplied after the OLED is fabricated either by printing on the backsurface of the OLED or laminating or joining without adhesive the OLEDto a glass substrate with a pattern on it. The pattern can be furtheroptimized for visual viewing. In particular, the dots can be small inthe center of the field of view because there is no significant angle tothe light emanating from the pixel and thus no path to the eye. In theperiphery of the display, the slight thickness between the lightemitting pixel and the blocking/reflecting element means the eye canlook ‘around’ the blocking element so they should be radially offset,optimally elliptical, and slightly larger in area. Note also, in thistype of display, the blocking elements should be absorbing in nature notreflective otherwise secondary reflections will be caused which willdegrade the contrast ratio of the displayed image. So, while reflectivewill work, absorbing is preferred.

In each of the descriptions of the system, the emissive transparentdisplay may be replaced with a stack of two or more such displaysseparated by glass, air, or another transparent medium. Thissubstitution enables the display and optical system to place the imagesfrom each of the display panels at different apparent distances from theviewer's eye.

In the case where the curved mirror is partially transmissive to enablethe user to see the real world and the images created by the display andoptical system simultaneously, it may be advantageous to place a meansto polarize the incoming light in a controlled way. This may beaccomplished via the addition of a liquid crystal type panel which has apolarizer on the outside surface but does not have one on the insidesurface. This enables a computer to control the polarization of thelight from the real world. That incoming light may then be passedthrough an optional wide band achromatic quarter-wave plate if the lightneeds to be circularly polarized to be appropriately transmitted by therest of the system. This enables the virtual images created by thesystem to be presented in combination with the real world where the realworld may be spatially attenuated if desired. Some liquid crystaldevices may be setup to directly impart the transmitted light with rightor left handed polarization, in which case the function performed by thequarter-wave plate described above and be subsumed into the computercontrolled device. This portion of the system would ideally be curvedand manufactured into the outer surface of the curved reflector andwould ideally have a shape such as to fit to the contours of the faceand the industrial design of the display system.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the inventions. Theelements of the various embodiments may be incorporated into each of theother species to obtain the benefits of those elements in combinationwith such other species, and the various beneficial features may beemployed in embodiments alone or in combination with each other. Otherembodiments and configurations may be devised without departing from thespirit of the inventions and the scope of the appended claims.

We claim:
 1. A method of forming an augmented reality displaycomprising: providing a curved reflector having an interior surface andan exterior surface; providing an optical and display stack comprising afirst display and a second display, and orienting the first display andthe second displays at a distance from the interior surfaces of thecurved reflector; providing a quarter wave plate and a reflectivepolarizer and orienting the quarter wave plate and the reflectivepolarizer between the first display and the second display; andproviding a liquid crystal shutter operable to adopt a transparent oropaque state and securing the liquid crystal shutter to the interiorsurface of the reflector.
 2. The method of forming an augmented realitydisplay of claim 1 further comprising: providing one or more additionaldisplays and placing each display at a different distance from theinterior surface of the curved reflector.
 3. The method of forming anaugmented reality display of claim 1 further comprising: obscuring thelight emitting elements of the display by a light blocking pattern. 4.The method of forming an augmented reality display of claim 1 whereinthe step of providing a curved reflector further includes forming thecurved reflector to include an inside and an outside and providing aliquid crystal display on the outside of the curved reflector tospatially attenuate the real world.
 5. The method of forming anaugmented reality display of claim 1 wherein the step of providing acurved reflector further includes forming the curved reflector to bepartially reflective.
 6. The method of forming an augmented realitydisplay of claim 1 wherein the step of providing a curved reflectorfurther includes forming the curved reflector to be reflective.
 7. Themethod of forming an augmented reality display of claim 1 wherein thestep of providing an optical and display stack comprising a firstdisplay and a second display further includes including a plurality oflight emitting diodes.
 8. The method of forming an augmented realitydisplay of claim 1 wherein the step of providing an optical and displaystack comprising a first display and a second display further includesforming the displays to be semi-transparent.